Transmission control



Nov. 3, 1931. R. c. MATHES TRANSMISSION CONTROL Filed June 11.

1929 2 Sheets-Sheet //v VEA/70@ R C. MATHES.,

AHORA/EX Nov. 3, 1931. R. c. MATHl-:s

TRANSMISSION CONTROL Filed June ll 1929 2 Sheets-Sheet 2 ATTORNEY V cir'cuit-conti'ol means at liajtcnted4 i 3,

iszases fi rrfri:NTv OFFICE u noBEn-T o. Marlins/'orf ifv onine,

'Jini-snif, AssIeNos To BELL TELEPHONE finnonsroains,"moonroias'rnn, or iimvoiax; N.' Y.; ficoaroiia'rronor NEW YORK i "Application 'sied Jiieii;

Y This invention relates :to-electric Wave transmission systemsf particularly to .two-

Way electricv communication systems. f.

The invention Vinits broad aspects relates A@to the controlling'oftransrnission in asignal fincluding therein circuitfcontrol'means operated undercontrol ofthe signals transmittedl over Vthe' systeniif f. The;invention is especiallyapplicable to la. system over WhichtWo-Way transmission of -si'gnaling energy is required Within the saineV frequen'cy range, and. including; asa link *therein a long sectiongof two-Way cable -of thighattenuation, lsuchgasj a deep sea `submarine cable. Signaloperated Vcircuitconfv v trol apparatus, foriexainple, sol-'called` singingfand echo Suppressors, kare usually asso- .'gliciated with. the oppositelydirected amplify-y :ing paths at each terminal, ofthe cable inssuch a system to insurefthat-the,system is operative to transmit in only `one direction `at atime7 so asto eiectivelysuppress echoes, singing or a f both. This is usually accomplishedby tmalr-l fininalresponsive to transmission in one direc, tioii'to make the circuits operativefortransmission in that one direction and to effective- Vvly disable'the circuits forftransmission in the opposite direction.y

af'system, the combination; of Wliich"mayiii-A Ytransmission' overvtlie xcable 'due toits 'length Ya'nd.lrading, and theotherL the hi a .ion o f the cable.1-

"hojcable greatly increasesl the chance that lo subscribers atopposite endsiof the eniniay both start' talking Within the f iteitval equal he'transmission timeofthe cable, resulting in-y each kvsubsc i'iber by means transmission system bycontr'ol energy transy ,1,574,781',' issued March 2, 1926 and agplicants U. S. Patent No. 1,67 8,188, issued Y ingthecircuitcontrol apparatus at eachfterA '.-trodiicediificulties in the application yof such .tiiereto. @ne ofthese islthe increased'time0f k'inifiilisiri-'issiou CONTROL,

1929. 1 seriai No. 370,034.

of his circuit-control apparatus securing con- .trol ofhisown terminal for transmitting and lockingcut the transmission received from theV other subscriber. In general, this condition mayY be avoided by circuits designed to f give kcomplete control' of the system to that subscriber at one end 'of the system Whose speechyenergy first reaches the cable.'r In the prior art, the U. S. patent tol Bartonl No.

i 1115' 24,1928 disclose certain methods for operating a plurality of repeater circuits connected in tandem involving the sending out of a sus* tained yalternating cur-renti Wave,-called the -c0urier,. under the control of the speech Waves, from eitherterminal over the cable or an auxiliary `circuit aheadofthefspeech Waves toicondition the 'circuits forvrepeating in the -properldirectiong A method ofthis general'.Y

nature is adapted for ruse in a'cable system such as described above, but must be'considei ably modified, because ofcharacteristics peculiarto the system `such as the very high attenuation, Y and; the limited, useful frequency.

range KVandload capacity of the cable, to make it practicabley for commercial use from the standpoint ofquality and economy. v, 'y

A Tooperate'such asystem it is necessary to have informationy at both ends of the cable as" to Whentalk is'going in at either end, and this information. must be positively received through talk going out from the other end.

The direction of energy flow is unreliable in v ygivingsuch information as the Weak speech *Y Y y. energy incoming from the cable atene ter- There are two main'characferistics lofy such with the'invention be carried by auxiliary Waves vunder -control of the speech Waves.

The diiflculty associated with applyingsuch auXiliaryWaves't-o the cable simultaneouslyu .l rv 'wi'thfthespeech Whose presencetheygare to Y rEhe increased time of, transmission iOfry indicate fis thaty theywill yuse up part ofthe load carrying Vcapacity of thetransmitting ampliiierfand, moreimportant still,V of the ie loadvcapacity of the cable, 1 if interference igsaaeosf t il insure; substantiali.;gconjugacy;V between Vthe i paths TA andi RA.; 'Fora Lsimilarpurpose -the input of the! transmittingf-pathfllni: and the output ofthe receiving path lRA' are connected to f the signaling lineTLthrough the hybr-idf coil Hg having a'n associated balancl 'fingnetworlrNa i d, H

` i .l I Connected between the hybrid coilslHZv and f' inthe'foneA-way path TA is Vafdela'yfwcir-v 'lo'cuit '16 and aone-waytransmitting amplifier 17, andconnected between the hybridfcoilsHl "and Hzin the receivingfpath l'tAjis afhandi f .Qpas'slilter'jand'theone4way receivingfame plier; 9. Connected' across the path TAat points between the' hybridfcoil. l H2' `and the delay circuit Gis acontrolcircuit 10.1comprisi y vice 11," and a' fa"stop'eratingl relayr 13 and 'al f, Y slow-operating relay-12 connected in parallel e ing' a current'K-contro'll'ed relay Controlling detothe output of thecontroldevieefll.'fA

2f Vsource 14 of alternating current of frequencies effg, which are outside thespeech.frequency.;

y range.l is 'adapted tobe momentraily con- 1nected across the transmitting path TA at the points 15in `the`-output of delay circuit 6 1 byjmeans of switches 16y and 17-control'led'by the operation of relays 13 and 12; 'Connected trolledrelay-controlling device20, andthe rea'yf21'y connected,y to the. outputy of control` de- Connected i'acrosstlie receiving path RA at lfpoints; 2 2between-ftheliybrid"coilH1, andthe i 1 filter-".8 Y'a 'thi-rd'fcontrolicircuit.23comprising vthe filters y24andlv25 connected in parallel, the 4' currentlcontrolled, arelay'r-control'lingl ydevice 26 inlseriesltherewith,-andg the relaysv -27 Vp-to 31 connected in parallelv to vthe outputl ofy control device k26.

switch32 incontrol path23`between the .out-

f-puts oflilt'ers 24 and 25 Vandthe inputof{con-y j' trol ,device 26.""'Relays27 to'311are`responf f Y sivey tothe operation 'of control-devicea re- Spectively to closetlie normally 1open 'switch 33 in the-outputof the yi"ecfeiviing annolifier` 9 in receiving pathfRA, toclose the normally f. switches V35k and '36in ftheftransniittingfpath TA, and `to openjthe normally closedswitch 37-in the output ofde'lay circuit-19incon- :uitrol circuit 18. Y

\ Although thej'receivingcircuitis shown :normally Vdisabled at asingle vplace -.g(nor mall-yV open 'switch-33),.'lbecause fthe vhigh v l gains-' whichfare'necessary ina system of 'the'v2 '-"Itype 'described it maybe desirableifo have n' It is apparentthatffthe terninal-fcircuit whichlhas just beendescribed is ofthe form which is lmown'in the art as semi-biased, that is, the Ycircuit isnormally operative to trans- .mit-in onedirection (in this case from east to west) and transmission inthe opposite di-f 70 rection '(in this case from West to east) is dependent upon :a switching operation.

y"Therelay controlling devices 11, 2G and 26 may be vacuumtube amplifier-rectifier de# vices of the'type wellknown in the art, or anyff35 other devices which will respond to alternating current impressed upon their inputs to controlthe voperation of switching devices,

such' asl mechanical I relays, in the outputs thereof.

lThe delay circuits 6 and 19 may be networks of anytypesuitable for producing. a delay 4of the required amounts, which. Willbe specyified below, inthe transmission of alternating currents impressed upon their inputs; for example, they may be low-pass electrical lilyters' such, as disclosed in U. S.y patents to `Campbell Nos. 1,227 113 and 1,227 ,114, issued May 22, 1917, acoustic filters, ornetworks for a similarpurpose such asdisclosed in Arnold,

Patentk No. 1,565,302 issued December 15,`

Filters k8, 24 and 25 may be of the type dis`` closed in the U. S. patents to Campbell, men-V tioned above.

The filter 8 and the filter arefband-pass filters designed to pass fre" quencies within the speech frequency range and to substantially suppress other frequenfcies, While filter 25 is designed to pass the courier frequencies f1 transmitted from'thef" leo n Westterminal station (not shown) and geni t erated-thereat byV a generator corresponding to the generator 14 at the east terminal stationfThe frequencies` f1 may be any fre-y -quencies outside thef'speech frequency range' and:differingl from the courier frequencies f2 Y f A v generated bygenerator 14. e n onslve to operation of the A d A control device 2`Oto openthe normally closed The one-.way amplifiers 7 and the retion may be of the system as whole will now be described referring to Fig. 1 only. Toaifd in ythislit will beassumed that tele- -phonic lcurrents for. transmission from east open Switch34 in theA output of'iilter`24 vin control path23, :to open` the normally closed to'west are received first at the .east'ter'minal 'station from the tolli telephone line TL, and

atsorne timeflater and within theinterval the hybrid coilHg. A-small -part of these currents willfbe divertedfrom the path TA the'v control circuit 10-and operate con-y l`ays'f12, 13, 214a'nd 27 lto 31 and the corre-y spending apparatus at the west terminalsta# Y any of the types'well lmown -in the fart 1 fj The operation of portion of the courier -q Vvric-rol V"demice llf thereiinjwhichi'n--.tu1f11`l will energize the windingsbt relaysil2 and 13;

, .Rel'ay13 will operate `quickly to l,close switclif v '2:16*'to-.,oonnect the .generator 14a-.across the the switclhvilrso as rto'dis'conneot the generator 1 21 will .oaluse're'lay 21 to'ope'ratetoopten thek 'transmittingv .pathy 5111A; Slow-.operating rre- -;lay.121Willeperategan; instant;v later to open i @1e/from the.path'TA..-;'The effect offthis l 'quick `connection Eto. and thezfollowing Vdisj" 4 l .y 5210 f vvegeneratofr' 14,'will'beto cause Yay short'impulse.`

off; current Vof frequencies fg to. be Vtransmitted out'lover; the pathfTAQ This impulse; or'4 conneetion: from'transmitting path -TAo i courier, :mayibei made as short A.as is desired orV 1s necessary by the'deslgn of relays .12 and i 13. .The :relays l2 fand-13 are so designed that y they. will remain. operated aszl'ong -as speech f 4"waves fromvthe'source"TL'arefbeing continuf- ,ouslyf' (supplied vto the' L'cofntr'ol,. device $11.." They'are designed softhat. they'will 'release .,fwords.

" V""liSh initial operation off thel switching oir-.1l ylouits'at thewest terminal stationinrv the mani ythecontrol' circuit 18.

` '-fonlya'fter a lcomplete .pause in the conversa .tion Ian'd1;not for ordinaryxpauses between A portion of the'coiirierffl will. be .ramplie` coil HAL/and transmitting thereover to estab.-

''ner Which-will be explained .laternv `Another f2' kwillbe diverted into thespeech currents espresse-a @emanati/ay .pani TA @brengt hybrid .'coilV H1; will passfthrou'gh'the delay .fcircuit 6 which lwill delay Ait in transmission Vbelf1`inf1-d the Vcourier.is only 'long enough tofin fsurecompletion offgfthe initial operation r' of .-'S'Witchingapparatusat the westtermina'l .sta- Y Y filter. 25. to the'inputof control: device 26.

ik l' ,f tion "bye the' preceding -courier/Q b.eforefthe i Y wouldbe-in theo aseeond.; a

The portiony of i voperates centrldevice20ljto energize the- *winding' of relay 21g -Th'efdelay circuit'v-l9Y yneed notfbea-.high grade one as-it isonlyre# courier f2, and visV maintainedoperatedby the way ef aceomplishing thlisris by relativelyde- `the" sensitivitiesof'the control' d normally closed switchr 32jincontro1-.cirouit f Y 23 and will,thereforegprevent:the operationy 75.

:of control-fdevice26 to operate yrelays 27,1301L "311, byVV the Courier fi; which lis. sent "out, from thefwestj terminal-station .inl response. to 'speech `waves Ithereatflater than thet courier f2V Y' ,..sent outfromgthe east terminal station.y f e, 'f -In the manner which has just been des'eribed 'complete control'ofathentalkingv cir` 'c'uits'of the east terminalstation has been obi v y .l i Thev manneriin whichY complete VControl of VVthe.' talking Qeircuits at fthe west terminal' is obtained for-,thersttalkerwhich in this l lcasellas been assumed tojbe the talker at-the lied-byfthe'transmittingamplifier vZ'f'a'ndrimg eastiterminalg'will, now be described.) Thatgl90 .f'press'edfon'the' .cable TG-.th-rou'gh the hybrid n west. terminal station lwillfjbe; indicated 'by quired forfthe purpose;Qfpdelayingan operatine" ll'pllse? Ehe 'contrer devise.- 20 .is only' initiallyloperated by lthe V.diverted .portion 'of' nected 2 thereto..

transmitting circuit in so l manyf".plaoes is re-r` 125 "speech waves 4whichv `follow -15 seeonds :later-.f

VVquired.toi-prevent false operation ofi, tliere'lay` Lydevice20l should be-Lj operated by .the l, speech wave' junlessgthe :control device 1l A Y*in 1 'l control pathvlQf-:hasbeen 'operatedg One the `.control devi'cef20; yin, control-,cireuitllf l The energization of the windingsjofrelay` .tained bylthewestwardly*directed .telephonie currellt'slatfthat 'station the apparatusto bereferredfto isthat `)of the designating. thev apparatus ithereati` withl the saine charac-ters'v whiohffdesig'nate I the.;v corretion and ini advance'of lthe 'speech' .wave by an V"interval ottime' t; onl its 'arrival iat the; .10Q

V'tilterff *receivingV path-RAgwillnetpass' the frequency f2s@ the courier will'beidiverted -at the points 22` into the'controlpcireuitgd 23 V'and' will 'be; vselectedY and, passed by the The transmitted .cdurier-f2 Will- "initially operate the' control .idevice 26': thus "energizing RAQmakingthat path operativel Jfor'y transmissiomof' thereeeived speech waves from hybridv coilLH'lrf' toH'z4 ;the operation, of .relayJ i 28 .will Close-switch34!'in@control path 23',

Y makin-g that pathoperative v:for the transmis-V Y sion of la portion ofthe received Vspeech currents tofthe'finpiitof feo'ntrol Vdevice 26"; the

cirenits Y associated therewith by. Unbalaned receivedenergyorby energy stored in .thedelay circuit-.6 previous to t e operationzof eon' soy spending apparatus at the east j terminal; sta-95 Qtionybutfollowed byagprime;(5)"Inarkg Q f .The .portion fof 'thevv .courier ifa'. whichk is transmitted over-thecable .-fromtheeaststav the .windings of; relays 27 *to 3'1"r and eausing. 1.110 these relays tofoperate. The operationof 11e-r l y lay-27. willfclose switch 33 `in receiving path "verted Vfrom'transmit.ting 'pathl VTA into oontrol circuit 18 is" del'ayed-therein-"by delay vcireuitfl lfor Tt's'econds-,whereT is Ythe'to-IV tal transmissiontime of the cablelTG'from i the eaststation to'the'west statioma'nd then;-

operation pf fiel'ays l 2955 130", and 31 will 're-f. .120 Yspeotively-` open the 'normally closed. switches Vv355 and ,V361 in. thel transmitting V"eireuit TIA" Y y ceived attlie West terminal station. 3o.

. tion'lrofycontrol device 267V cannot Vget 'through toop'er'ate'control device 20 'and therefore y relay 2l" to' disable thecontrol path23by Thespeechwave transmitted.from-.theeast terminal station over the cable' TG i? seconds behindthe courier f2fonfits:arrivallat the; West terminal stationwill impressed, ,onl f the receiving path RA thereat bythe hybrid n coil H1, and will divide at .the pointsL 22" between the .control circuit 23, which 'passesv boththe control frequency 72 and the -speech ,34' Vin the output of filter 24no-vv being in upon the inputcircuitv of control device mainta-iningthis device inits operated con# 'dition' initiated i yby the preceding (courier,V Y ,if thel speech waves'p'assed by filter 24," havek f not .beenpreceded bythefcourier impulse f2, they will, not get throughftofoperate control device 26 because the switchv28 in the input of control device QGyvillbe'open, The c onf.- :trol of control, device 26' by 'the' speech Wave will cause relays 27( to 31 tobe maintained`fl l in the operatedcondition asp-long asthe WestvfardlyV directed 'speeclifwave is beingfrev Becauseof the openingy ofthe switch 37 :in control path`18 byoperation ofthe switch 3l', any energyvi'vhich" might be stored ini ydelay circuits-Wand' `191,".prior to the operaopening the sivitch`32AV therein.

n The transmitting aiid 'receiving circuits" of both thev West terminal' station andthe --east terminal station are now 'under complete control yof, the east terminal station.y

It is readily seen that because of the relaf tion specified o f the delay timesin the'delay circuits 6. and 19 at the east terminal station and 6,', 'and' 19 at the West terniinalj station tothe transmission 'time of the 'cablef 4TC,l that whichever terminalfirst sendsout its L courier will gain exclusive"control o sets of terminal apparatus. A

'if Vthe oppositely directed speech" vvafve both . lfromthetwo talkers at the tivoends ofthe system "reachV the twoterininalsi almost simultaneously, but th-e eastV ta-llerJst-arts 'aheadof the West talker, the c'able'TCWill be charged With loutgoing transmission from the West k'talker at the tiniefcontrol device 26 at the West station operates. Incoming speech at the West station, therefore,fWill/be mashed by the V4reflections 'from' outgoing' speech during the time it takeskv the ycableto y dissipate the portion of the'outgo-ing speechfen'ergy. rThis Ameans thata 'small amount of the speech may be lost ordist-orted if the system ofthe i invention is used.jfThis loss or l'distortion will. not be sufficiently be trouble-- some inl practiceunless a very high grade of quality 'is desired,`es'pecially`as such'floss will,

occur, relatively infrequently.

' In the system 'of the'l invention.l it` may be t necessary to receive the incoming 'couriers f1. j 70 and fgfatfthe"terminals ofthe cable'in'the presence of simultaneous"outgoingl speech energy, The filtersV and other apparatusin' the system should be so designed that the courier may be separatedffrom the speech energy,y and so that the'outgoing courier or spee'chdoes not falsely operate the receiving conti-ol apparatus. This'should not be' diiii#` cult if the cableTC'is not too long or oftoo high attenuation, or if. modulation products ofthe speechfrequency fall Vat 'the frequencies 'f1 and f2. i 3 shows an intermediate repeater staf" tion which is designed tooperate ina system l having 4 terminal stations such as has been describedinconnectiontvith Fig. 2 and Which connects'tWo sections of the cable T G' which Willbe designated as TG1 andy TG2 respective-Q ly@y The, circuits, of the repeater are soldesigned lthat' the terminal station'vvhich first.

sends out yits courier willobtain exclusive control of the circuits of the intermediate" jrepeater as Welles the circuits of the two terminal stations. Moreover, the intermen diaterepeater station isfarranged so that any lossof spech'during the discharge time of a cablesection is avoided. y

V,It Will be assumed that lthe sectionof the cableflG1 joininv the West terminal station and the intermediate repeater stationhas an overailltransmission time-of T1 seconds for the currents transmitted thereover, yand the section of thevcablelTCZ joining the east ter-` mina'l4 station kWith the intermediate repeater station has an overall transmission time of T2 sections for currents transmitted thereover. Y

" The intermediate repeater station comprises, connected between the two cable sec! tions T'Cl' and' TG2, a `Westivardly directed yamplifying path VVA-and an eastwardly dition CA in common.` The path VA comprisesin order reading from east'to West the one-Way amplifier 38, the bandipass filter 39, the vdela-y circuit 40, andthe' one-Way amplifier 4l. The `ainplifying path EA com,- prises in order reading from vvesttoy east the one-:Way amplifier 42, the band-pass filter 39, the delay circuite() and the one-Way amplifier 4l. 4 The one-Way amplifiers 38 and 42 in the amplifying pathsVVAl and EA respectively are utilized forthe purpose of enabling trans-v mission from either path WA or EA to be'` supplied to the input of transmittingamplifier ilL in the common path CA Without getting over into the other amplifying path; Other means may be used forthis purpose, for example, a balanced bridge'suchfas dis'- tween able sections' TC; -and' TClin theo'ute f The Y p lifyingp is knornffally i traii'smissionfrom;east"tOjWestbe ofltheampliiier vllby the normally open openfsvvitch controlled 4by the ".relayfe46.

' We in theinput ofthe a'mp1:L el'Y 38 therein.`Y '1 .Siinilarlyg {afj normally closed switch 49 4'con-l l? @meaty the reiayoa located in ,the ampli-,

fyinggpath E Ainthefinput of the amplifier..l

" "i substantiallyequal to TZ-'T'Tl secondsFor v Y ;,.-Connected 26 andthe cablesectionTCzis ya vvestyvardlyidi-k l rected'onefwayfauxiliary pathC-l comprising between the cable., section TG1 the ydelay circuit 51 and the .one-Way lter 52, andan eastwardly vdirectedone-Way' auix-, iliy' p'at h Ggf comprisingthe delay circuitv i' andthe one-Way filter 54.]A normally?.

.closed Vslvvitchj controlled by a'relay 56f is l "or received at vtht-feast terminal station first,

located inthe pathf C1 betvveen the input 5 of` the ilter52-and V.the output of' delay circuit i z lftherein. `Similarly," anormally 'closed vilterl.andthe output of delay circuit .531 y Y Y i' transmission from'ivvestltoeast. v Inthe man-y f relay fcontrollincr device 6 2Which controls Y vthe operation o i f shovvnA in Fig. 2. j Y The,'filters39,V

. areV similar tothefcontrolling devices ll,

Oiswitehfstcontrolled bythe relay 58 is 10-1 cated 'isf path o2 betweentheinpat or the therein. Y f f A; Y- A control-pathrfs faninectedl to thepath;

In thecontrol path is a current-controlled Y i f -relays '46', 48 land' 56. Thegrelay controlling devicesv {Sl} and G2 Y.

and 26 in; the circuits of the terminal station are the 'filters at '-the terminal stat'ionfshown in quenciesvvithinpth'e .speech lfrequency range j' "and Vto su'ppressthe couriergfrequencies f1 and;f2'. Filter 52 iszdesigned ,to pass courier Yfrequencies f2, and to suppress courierfrequencies f1 andwaves 1n lthe speech-'frequency i f The, delay circuits 40, odiare simis larto thedelay circuits at the terminal sta',-y

tion shown 'in Fig. V2. The delay circuit 40 l 1 Y isfde's'igned toiiitroduce a time delay in Waves Within the speech frequency range equivalent issued Decemberiajieae transmission; time;T1k fof l:cable "section, TG1 is greater thanthe transmission timef'lzv of cable section TG2, then the delay ltime of Vd eylaycircuit 40 shouldbejTl seconds. vOnthe Y to"fthatifintroeluted;V the the longest A'time' off. transmissionf If; the

other hand, if T2 is greater than T1 A:then the cuitfjil should lbe substantially equalV to is greaterV than T51, fthe f delay; time Soffdelay circuit 51 should befsubstantially yzero-and the delay timeofl delay circuit should b e conveniencein describing -the' operation of the 'intermediate repeater station, vit 'will be.

.assumedlthat Tlis greater thanT2. 'For this `case they vdelay times of delay circuits-40, 5 3 k and 5ll should be" i substantiallyy 'll, O, and 'Tlf' T2 seconds, respectively. I *Le't itl-be assumed that speechyvaves for transmission from east to -West,aregei ierated n'er described in connection TTwith' Fig. 2 fthe Y speech Waves at the east `terminal`station will cause the courier of frequencies'f2 to be geni .y out over. thecabIe section;l TG5 in fthe' 'direc-Y vtion 'east towest-aheadfof the Vspeech Waves by 'the time''interval4 t. At' the intermediate repeater station: the courier fzv'vill be divided betweenthecontrolpath vC1 and the am plifying path WA; The portion of courier 7'2 in amplifyingrpath" WA. Will be dissipated etk thereinV as the band filter 39 therein isdesigned to suppressfrequency f2. .The portion of Courier; fgk ydivertedinto control path Cl Willbe y'passed through the delay circuit 51 being delayed therein for T2 seconds.' The passedl courier will divide-inthe input D fgiilter '52. iA-portioiitlie'reof Will' befpassed section .TCfand'transmitted Athere'over' `to ess- Vtablish initial control of the transmitting and of speech Waves from cableTC-to cable'jr'ICl.Y L The relaysimi'iltaneously operates to'open-Q @5" The courier f1 and im "son `the'normally closed svvitclilt) inamp-.liiyiiig Y pathk EA disabling'thatpath' for transmission trom''cable. section' T G1' jto :the inputot anipliiier i2 therein. The relay 58 'simultane- 'oiislyv operates? to open ithernormalily closed v sivitchif'in cont-rol pathlY-Ggto disable that path for transmission .oftheV courierk f1 or the succeeding speech Waves Jfrom 'the West terrminalfstation to the .inputs ot iilterefand licontrolldevice' 4^ Thespeeeh wave ypath/G1. .A1 sinall .portion/of these' speech. Waves Wil-l be passedbyidelay circuit 551 the path G15 diverted` intocontrol path 59 and Him-pressed on the input-otcontrol device $6.1'

'causing that device toibelmaintained in. the

p operated ycondition' initiated by the preced' ing courier f2 aslongas speech is beingftransmitted trom easttorvest,V .Relays44,50 and 158v there-tore Will remain intheY energized con- E lditionftor that length' ottime.

i -1 The main portion 10i the speech Waves received over' the cable lsection TG2 ltrom the east terminal stationwill bev diverted into the main amplifying Vpath WA. This portion ofthe speech Waves Awill be amplified by am Y p-liiierBS, passedby band-pass filter 39' i 4`after a delay of T11 secondsfxin delay circuit lyrvillgbe lamplified by amplifier eilandi' v trarisnciitted directly to cable section TG1 and over f thatcable sectiontof the West terminal v i station. Apt the West' terminalwstation a small g portion Y'ot the received speech'jwaves are ntilizedvto maintain the switching apparatus y thereat in the operated condition initiated by:

ie 4the preceding courier riii-'eqiiency and the main portion of rtlie'received speech Waves Will be transmitted:to l the receiving appa-x ratus,;inthe mannery describedwin' detail in connection with Fig. 2. A y A its succeeding West-to east speech Wave troni the West station, be-

1 cause they are fsentouttheretrom? later than the courier fgand the speech Wave from the east statiomwill not be eective on arrivalat "tlieinternediate repeater station to aite'et' the i n operation of the control apparatus therea't or i to get-.throughtothe cable section TG2 be cause thesvvitchesf-Q and lin amplifying ,pp ath' EA, andthe svvitch? lin the pathy G2 i V5 f5Y-a`re Vopen atthe ytime of their arrival thereat. l Itis apparent from the operation described thatv :control ofthe transmitting and receivinglzcircuits otboth terminal stations and the] "circuits 'jot the intermediate repeater station:

Y, f" has beenvobtained for the east terminali stay tion, that is, orthe station ativhichthe speechlivaves ortransmission to the other I station werev iirst `received or generated. g The delay in.- transmission "of tlie=-y s'peecl'il 556511* currents from east to west over thef amplify-l tr ansmitted 'from the eastzl yterminal station .over cable section TG2 t' sec-A onds behind the` eonrier on arrival atthef l A intermediate repeater station Will be divided 1' ing; paaifwa .provided by; the 'deity Circuit L 40; .whichxis equal to.- the .time of transmission over that onefot the Vtwocable sections Which ha swthe: longest-transmission time (in theV case assumed 'T seconds) insures that the speech Waves follow the preceding courier i oier.- theicableseetionl*TGlrwith suiiicient lag toperinitany speech energy'onVthat cable section to bedischa'rged after the courier has-xobtainedgconti'olfof the distant station7 and tli'u'saprevents loss ofspeech during the discharge timefof thecable section. 4 Y

:Whenfspee'ch .fcurrents are generated or receivedfat ith'e' Avvest* terminal u's'tation for ytransmissionitroinWest to east `before theoppositely'fdirected speech currents are gen' erated For; received :at the east terminal sta@ tion, the courier f1 and the succeeding speech Wave on their arrival at the intermediate vrepeater station control overpath G2y and con-l trol pathGOQthe operation of "control device GQ'tooperaterelays 46, 48 and 56 in a mane ner similar tothat described in connection f Withtlie Westivardly' directed courier f2 and theVv Westvvardly directed speech Wave; to make operative theamplitying path EA. by

- closingiswitc'h 45- -therein,.to disable the am plifying path *dinghy opening the switch 47 thereinyand :to disablethe eastwardly .di-

rected path G1 vby opening. the sWi/tc'hy therein. Gomplete control voi' the internie'-v i difaterepeaters circuits for the West terminal t-is-lto be understood that the invention iswgeneric in character and is not limited to thevparticiilar circuits and details of the terminal "and intermediate repeater stations illustrated and described since numerous modifications therein'may Vbe made by persons skilled in the art Without'departing from thespirit and scpeottheinvention. For examplethe terminalfcircuits illustrated and described comprise afnormally operative transmitting circuit,y ak normally disabledreceivingcircuit and switching means respon# siveE t'oenergy received over the cable forl disabling the foi-mier and making operative the latter. n

It is, of course,y apparentI that V'the invention is applicable as Well tof-such circuits modiiied soV as to comprise a normally disabled transmitting'circuit, a normally operative receiviii'gy .circuit and switching means respoii sive toienerg'yto be transmitted to makeop-` erati-ve' the' former 1 and to ydisable the latter; or ftofcomprilse areceiving cireu'itand a transthe speech V*wave to initiallyoperate said circuit-control means in the proper manner, and

utilizing tlietransmitted speech variations t as they arrivent thegcontrol'points to maintain the circuit-control meansin the-initially operated condition. y y 9. In atwo-way telephone system compris- Y ingv signalf; controlled switching apparatus at various points thereinfor conditioning said f systemri'or efficientioperation; in the direction'fof ,speech wave transmission therein,.the

" metrodof opera-tieni which consists invv uti- A 2ov direction, and utilizing the transmittedspeech variations-as they arrive at the switchf Y ring points Jtoinaintain theswitching appai ,-25

lizing the speechfwave. at its arrival atone point in the system tof-transmit a momentary impulse of control energy. over the system ahead of 4.the speech AAvariations, toy initially operate the switching apparatus in the proper .raus in the initially operated condition.

.10 A transmission systemcomprising a signalftransmission "path supplied from. a sourceof signals, circuit control means in saidtpath for' determining the operation thereof, means underthe control of the supplie'(tl-signalsn for transmitting an impulse of current over sa-idpath ahead of said signals to initially ope-rate said control means, and

meansfor vutilizing the signalsy When vthey arrive at'ithe'control lpoint to maintain said `controljmeansjrin itsV operated condition.

f f1.1; A Vtransmitsslionfsystem. comprising ay signal transmission path supplied, from a i l source oisignalr waves,` current-controlled .means insaid transmission Ypathtor determining the'operationthereof,means u nder the control of the vsignal ,wave for sending over said path and in advance'oi the signal waves an impulse of current to initially operate said vcurrent-controlled means, meansto delay the 'arrivalpofsaid signal wave at the control point at least-until said current-controlled "means has been initially operated, and means forv utilizing thefdelayed signals when they arrive at said v control point to maintain said :current controlledfmeans in its Yoperated condition@ f p ,i l

- 7125A system for; the two-way transmission 'of telephonie currents including current-controlledfy switching means at' various ypoints therein-tor conditioning the system for ef- Y icient operation in thedirection of trans- 'mission`,"means at afpoint in the system and Y .controlled by the telephoniccurrents when vC0 they arrive at said. point, for causing a concontrol current tothe transmitted over the' system ahead of Ithe'telephrmic currents to initially l operate'.the-switching means in its path, and means for utilizing the telephonie currentswhen they` arrive at the switching switching means in its path in the properk manner, and means for utilizing the tele- Vphonic currents when they arrive at the switching points to maintain the switching lmeans in its initially operated condition.

14. A system for the two-way transmission of telephoniocurrents includingv current-con:-

trolled switching means at various points therein for conditioning the system for eficient operation in' the direction of transmission, means at a point in the system and jcon- -trolledby the telephonie currents whentliey arrive Vvthereat for causing a momentary impulse of, control current to be transmitted over thesystem to initially actuate the switching means in its pathin the desired direction, means for delaying the arrival of the telephonic'currents at the switching point until after the switching means has been initially operated by said impulse, and meansforutilizingfsaid telephonie currents when Ytheyv arrive at said switching points to maintain said switching means in the initially operated condition.

15. A system for the two-way transmission of telephonie currents comprising a two-way line,istati0ns at various points along said line comprising oppositely directed amplifying paths for said currentsconnected to said twoway line, switching means at said stations responsive to transmission in one ot the amplitying paths thereat for disabling the other of said paths, meansat one of said stations and controlled by the telephonie currents in the amplifying path for one direction thereat for causing control energy to be transmitted in'said one direction oversaidy system ahead of the telephonie currents to initially operate the switchingmeans in its path lso as to condition the system for eiiicient transmission of the telephonie currents in said one direc- Ycontrolled switching means at said stations and responsive to transmission in said system 23. The system of claim 22 and inwhich the delay means in the first mentioned controlcircuit delays lthe transmission of the wayes'therein for substantially T2 seconds and the delay means in said second control circuit delays thevwaves therein yfor substan 'tially T1 seconds, where T1 and T2 are respectively the overall transmission times of the west and east'two-way line sections. l

' 24. The system of claim 22 and in which Y the delay times of the delay-means in the first mentioned and said second Control circuits are T2 and Tlseconds respectlvely, where T1 and T2 are respectivelythe overall transmis- Y lslontimes of the westl and east line sections, v and the delay time of the delay means in each of the, two amplifying paths is equal to the yoverall transmission timev of that one of the LIN - l two line sections which has thelongest time f 

